Device and method for fixation of airframe pieces

ABSTRACT

A method for regulating a device ( 2 ) used for fixing aircraft airframe pieces in connection with assembly of airframe parts ( 21, 22 ), where the device consists of a rig ( 3 ) comprising a matrix of rails ( 7, 8 ) that can slide in such a way that a number of fixing elements ( 9 ) attached to the rails ( 7, 8 ) can be positioned freely along three co-ordinates x, y, z in space within a given volume, where a manipulator ( 1 ) grasps a fixing element ( 9 ) after which the fixing element ( 9 ) is moved by the manipulator ( 1 ) to the given co-ordinate, and where the rails on which a fixing element ( 9 ) is arranged is locked in relation to the rig ( 3 ) by an automatic locking function initiated by the manipulator, thereby fixing the fixing element&#39;s ( 9 ) position in space and the setting procedure is repeated for a predetermined number of fixing elements ( 9 ) on the rig.

TECHNICAL FIELD

[0001] The invention relates to a device and a method for regulating adevice designed, for example, for holding a number of aircraft framesfixed in a predetermined position and for fixing the skin of theairframe in a predetermined position to allow the skin and the frames tobe put together to produce an airframe section. The device can also beused to hold the airframe section in a predetermined position when partsare being fastened to the airframe section.

STATE OF THE ART

[0002] In the production of airframes, there is a need for some form ofwork fixture or jig, designed in such a way that the frames and the skinof a airframe section can be held firmly in place, at least at a numberof points within a given volume, so that the frames can be fixed inpredetermined positions and so that the skin of the airframe section canbe applied to, fastened to and be held in place against the frames whilethe frames and the airframe skin are being fastened together. In theproduction of aircraft, for example, work fixtures are manufactured foreach section of the airframe. Conventionally, a different work fixtureis required for each type of airframe section, so that a large number ofwork fixtures are needed. These are designed so that a rig with aframework is welded together in such a way that a number of attachmentpoints for the frames of the airframe are incorporated. The attachmentpoints associated with a specific frame are measured with a high degreeof tolerance.

[0003] Fixed conventional work fixtures as described above can only beused for a specific airframe section, which means that a large number ofthese fixed work fixtures are needed and that they can only be used forthe aircraft for which they were originally produced. This is veryexpensive, which means that fixed work fixtures can only be used forairframes that are mass-produced. In principle, a fixed work fixturedesigned for a specific craft can never be reused, and as a result isscrapped when production of the aircraft has been terminated. Somesemi-flexible devices are available on the market. These work fixturescan be adapted and used for several airframe sections. An example ofsuch a semi-flexible device is given in U.S. Pat. No. 4,695,032, whichdescribes a semi-flexible device for making a mould. A number of bars ormain rails are fixed to a framework. Supporting rods hold up the fixingelements, whose positions can be varied in the axial direction. Althoughto some extent the described device allows the points of attachment tobe individually set, the device is only partly flexible. Rigging thedevice is conditional on defining the position of the main rails and theguide rails before setting of the axially mobile fixing elements.

[0004] Another example of such a semi-flexible device is embodied by amechanism having a horizontal worktable. The worktable comprises anumber of rows of holes, which are arranged both lengthways andcrossways on the surface of the table. The holes are designed to providea support for upright rods, which can is be positioned on the tablesurface in the number required. When this device is to be rigged for anumber of frames that will be used to support a section of the airframe,the said rods are positioned in rows on the table in positionscorresponding to the frames' reciprocal positions in the airframesection. Each rod comprises a vertically movable fixing element, whichcan be moved vertically by means of a servo-motor belonging to each rod.For each row of rods corresponding to a frame's position in the airframesection, each rod's fixing element can, by means of the servo-motor, bemoved and held at a height corresponding to the height required for theframe to be supported by the said rods. In this way, all the rods'fixing elements can be set to produce a shape corresponding to thecurvature of the different frames, after which the frames, one at atime, can be fixed at the correct relative distance and be supported bythe rods at a number of supporting points in the fixing elements,whereby the frame retains its shape and together builds up the spacegeometry that the skin of the particular airframe section is to have.Then the airframe section skin can be positioned against the fixedframes and be fastened to them, so that the frames and the skin arefitted to each other when they are being put together. A disadvantage ofthe semi-flexible solution described here is the high cost since eachrod referred to above is supplied with a separate controlling mechanismfor positioning the fixing element at its right height. Furthermore,there are practical difficulties caused by the plethora of cablesattached to each rod for power supply and for controlling thepositioning mechanism. Nor does the technical solution involving placingthe said rods in the said rows according to a matrix permit variablesetting of the fixing elements' positions.

[0005] An alternative model of a semi-flexible device employs, in asimilar way to that above, a number of rods positioned in a matrix, i.e.in rows on a work table, but does not use individual power units forcontrolling the fixing elements on the rods when positioning them.Instead, a moveable portal is arranged above the work surface. Thisportal can be moved across the work surface and be positioned above eachrow of rods. The portal's overhead frame is equipped with one or morevertically operating arms, which are designed to move down to and graspa fixing element at the top of a rod. An arm, which is automaticallycontrolled by a control program, is then able to set each rod's fixingelement at the correct height one row at a time. By locking the fixingelements to each used rod according to this pattern, the rods cansupport curved skins or other structures with good tolerance. Adisadvantage of this semi-flexible device is still that the position ofthe rods in the horizontal plane can not be varied freely. Moreover, theportal robot that is used is expensive and cannot be used for tasksother than those mentioned, i.e. a manipulator in the form of the portalrobot is just as specialised as the device itself.

DESCRIPTION OF THE INVENTION

[0006] According to an aspect of the invention a method is provided forregulating a device used for assembling aircraft airframe pieces, wherethe device consists of a rig comprising parallel main rails that canslide parallel to each other along the rig along a first co-ordinate x,and where each main rail has a number of parallel guide rails which canslide parallel to each other along the main rail along a secondco-ordinate y, and where in addition each guide rail can slide axiallyalong a third co-ordinate z, with a fixing element at the end of theguide rail, and where the method involves a manipulator grasping a guiderail's fixing element after which the fixing element is moved by themanipulator in directions x, y and z so that the fixing element is madeadopt a predetermined position in space, and while the fixing element ismoving:

[0007] the main rail to which the fixing element is connected is slidparallel to the x direction when the manipulator sets the fixing elementat a given x coordinate,

[0008] the guide rail to which the fixing element is connected is slidparallel to the y direction when the manipulator sets the fixing elementat a given y coordinate,

[0009] the guide rail is slid axially in the z direction so that itsfixing element is set at a given z co-ordinate.

[0010] Additionally, the method involves the manipulator moving in turnto each remaining guide rail fixing element which it grasps, after whichthe fixing element is moved by the manipulator in the y and z directionso that the fixing element is made adopt a predetermined position inspace and during this movement the guide rail to which the fixingelement is connected is slid parallel to the y direction when themanipulator sets the fixing element at a given y co-ordinate, and theguide rail is slid axially in the z direction so that its fixing elementis set at a given z co-ordinate. All of the above steps are repeated foreach main rail until all fixing elements being used are set in thecorrect position.

[0011] When all fixing elements are positioned a frame is fixed to thefixing elements of each main rail after which an airframe skin is heldin place against the frames by chucking to allow assembly of the framesand the skin. Conversely, an airframe skin can naturally be fastened toand be supported by the fixing elements, after which the given number offrames are braced to the skin, thus ensuring that skin and frames arefixed in relation to one another during assembly of these parts.

[0012] The invention comprises a device for implementing the methoddescribed above, as characterised in the independent claims.

[0013] An advantage of this method of assembly is that the device allowsvariable setting of the fixing elements.

[0014] The manipulator used in the above method is preferablyconstituted by an industrial robot. Employing such an industrial robotas a mechanism for regulating the fixing elements involves firstentering into the robot's control system data on the orientation of therig in relation to the robot. This is done, for example, by making therobot hand, with or without attached tools, detect one or more referencepoints, accurately measured, located on the arm of the rig. A referencepoint may consist of a square plate whose position the robot hand or therobot hand tool detects mechanically, whereupon the position data forthe reference point in the form of its x, y and z co-ordinates are sentto the robot control system.

[0015] In the normal state, that is when no adjustment of the device isbeing executed, each main rail is locked to the rig while each guiderail is locked to a main rail Is by some type of locking device. Whenthe device is being regulated, these locks are unlocked by themanipulator.

[0016] A coupling is arranged between the robot's tool shunter and thefixing element. This coupling may consist of a female part arranged onthe fixing element and a male part on the tool shunter, which engagewith one another when the robot grasps the fixing element. The couplingcomprises one or more connections for engaging the guide for the lock.These connections may be embodied by pneumatic connectors for pneumaticor hydraulic unlocking via the manipulator, or electrical connectors forcontrolling electromagnetic or electromechanical unlocking devices viathe manipulator.

[0017] An advantage of these connectors is that the power for unlockingthe lock can be transferred and controlled by the manipulator withoutthe fixing elements being effected by any force that can disturb theirpositions in connection with locking. Electrical, hydraulic or pneumaticenergy is transferred via the coupling from the manipulator to thelocks, where the manipulator merely operates as a conveyor of the energyrequired for unlocking. When the said energy is no longer being conveyedvia the manipulator to a lock, the said lock reverts to its lockedposition. This type of coupling may be used for regulating the fixingelements, even if the manipulator is fixed to the device, in the form ofa portal robot or equivalent, or is manually operated and employsexternal measuring systems for positioning the fixing elements.

[0018] An advantage of this locking function arrangement, where thepower to unlock the lock is conveyed via the manipulator, is that thereis no need for cabling inside the device, which would otherwise berequired for transferring power to each individual lock.

[0019] Other advantages of the method and the device in accordance withthe invention is that the device can be simply and quickly adjusted fornew types of airframe. Consequently, the device may be used for morethan one series of airframe, and in addition, it allows an airframe tobe altered relatively easily and cheaply after production of a number ofunits in a model series. Furthermore, the same device can be used fordifferent sections of the same airframe. The device may also be used inthe future for products that at present have not yet been developed, andso can be used over a long period. Thus, such a device would beattractive in the small-scale production of vehicles and otherstructures, where it is not economically viable to employ fixed workfixtures or expensive semi-flexible solutions. In the case where anindustrial robot is used as a manipulator for regulating the device, theinvention method is particularly useful, since such an industrial robotmay be used for other types of work when regulating the device is notbeing carried out. Examples of such work are programmed drilling,riveting, and grinding on the actual structure or airframe that is fixedto the device.

[0020] The principles of the lock will not be further described in thisdescription, since they are already well known. Such locks may beembodied by work-holders or other friction locks, which using springforces, for example, hold cylinders or feathers under tension and exertforce between locks and rails. By applying a force against the springforce using, as mentioned above, pneumatics, hydraulics orelectromagnets, the work-holder can be released.

DESCRIPTION OF DRAWINGS

[0021]FIG. 1 illustrates the device and an industrial robot workingtogether to set the fixing elements on the device rig in accordance withthe invention method.

[0022]FIG. 2 shows the same device as in FIG. 1 from another view, andwhere additionally an airframe section is fixed to the positioneddevice.

[0023]FIG. 3 is a schematic representation of a guide rail with itsancillary fixing element.

DESCRIPTION OF THE EMBODIMENTS

[0024] A number of examples of the invention are described below withthe aid of the attached drawings.

[0025] In FIG. 1, the method and the device in accordance with theinvention are displayed in a perspective where it is shown how anindustrial robot 1 is used as a manipulator to adjust the device 2, sothat it can accept a 3-D structure in order to hold this structure fixedduring one or more steps in the assembly. The device is comprised of arig 3, which in this example is vertically mounted on a floor. Ifrequired, the rig may be built with a second level. It is possible, forexample, for several rigs to be erected in the form of a prism, if anentire airframe is to be constructed simultaneously around these rigs,where the rigs make up the lateral surfaces of this prism. The rig 3 hasa frame 4 with an upper 5 and a lower 6 longitudinal beam. These beams5, 6 function as tracks for a number of main rails 7, which are arrangedparallel to one another and where each one has a slide attachment withtheir ends in the upper 5 and lower 6 beam. Because of the slidingattachment, the main rails 7 can move parallel along the rig with theends of the main rails running in the beams 5, 6. The sliding attachmentbetween beams 5, 6 and main rails 7 also comprises guiding means, sothat the main rails 7 run perpendicular in relation to the beams 5, 6.The ends of the main rails run in the track-like beam by means of aslide bearing pilot, guide bar, guide roller or some equivalent knownmechanism. An important feature here is that there is a lock between thesliding, or roller bearing mechanism belonging to the main rail, and thebeam, so that the main rail can be locked and be held fixed in apredetermined position. This type of lock is known and may be embodiedby clamping sleeves, which via spring forces are pressed in and exertfriction between main rail and beam for the period of time the rails areto be held in a fixed position.

[0026] Each main rail 7 is equipped with a number of guide rails 8,which are attached with a slide bearing to the main rail 7. The guiderails 8 are arranged perpendicularly to the main rail 7. The guide rails8 can slide parallel to the main rail 7 and can also slide in the axialdirection. The function of the guide rail is illustrated in more detailin the drawings. The three directions of motion shown for the guiderails define a system of co-ordinates, where the main rails can be movedin the x direction along the beams, while the guide rails can be slid inthe y direction, that is along the main rails, where the direction ofthe main rails defines the y direction. The axial motion that the guiderails 8 are capable of performing takes place in what here is called thez direction.

[0027] Each guide rail 8 has a fixing element 9 at its end. This fixingelement 9 is intended to comprise the attachment points for thestructures, such as frames or airframe skins, that are to be held inposition by the device. Thus, the fixing element may be provided withscrew holes, rivet holes or their equivalent for engaging againstcomplementary means of fastening in the airframe structure.

[0028] The guide rail 8 has sliding bearings in a carriage-like device,to which we give the name carriage 10. The carriage 10 slides along themain rail by means of guides 11 that run along a conduit inside the mainrail 7. The guide rail 8 can be moved in its axial direction by a firstslide bearing 12 and a second slide bearing 13 in the other end of thecarriage 10.

[0029] The guide rail 8 is locked in a fixed position in relation to thecarriage 10 by means of a locking function. The locking function can bedesigned in a number of different ways. Locks of this type are known andmay be embodied by clamping sleeves, which via spring forces are pressedin and exert friction between the carriage 10 and the main rail 7 aswell as between the carriage and the guide rail 8 for the period of timethe rails are to be held in a fixed position. Since the technology ofthe aforementioned lock is well known, they are schematicallyrepresented in FIG. 3, where the position of the lock is indicated byarea 15 and where, in this example, it is also assumed that the lock isunlocked by compressed air, which is fed from the robot via air ducts inthe guide rail and then via air hoses 14. Thus, the robot 1 is passiveduring unlocking and locking of the rails 7, 8, that is to say the robotdoes not transfer any mechanical force to the device, although it doestransmit the power effect of the lock by switching on or off aforce-exerting medium, carried out in the example by pneumatic power,but where hydraulics and electromagnetism may also be used. In this way,the risk of disturbing the set position in which the fixing element 9 isheld by the robot 1 is reduced during the locking step in the settingprocedure.

[0030] The main rails are designed so that they slide in the beams 5, 6using a similar carriage design as carriage 10, and which is notdescribed further here. Even this carriage design may be locked in theway described above. The locking principle can be varied mechanically inseveral ways. Clamping sleeves can be used, for example. Unlocking isperformed according to the above principle, where even in this case thecompressed air is regulated by air hoses from the guide rail 8 to thelocks at the ends of the main rails 7. By regulating the airflow fromthe robot via the guide rail 8, the main rail can be unlocked completelyby supplying compressed air to the main rail's lock.

[0031] The method according to the invention for regulating the deviceis exemplified and illustrated in FIGS. 1, 2, and 3. These drawings showa manipulator exemplified by an industrial robot 1. The robot 1 ispreferably transportable on a track alongside the device 2. The robot'scontrol system is supplied with data on the intended airframe's shapeand thus is supplied with data relating to all fixing elements'requisite positions in space as given by space co-ordinates. The robot'scontrol system is also calibrated with its own position in relation tothe device 2. This is achieved by the robot hand 17 seeking a wellmeasured calibration plate 18, so that the robot hand can sense theplate's 18 position, thereby allowing the robot's control system to readthe relative positions of the robot 1 and the device 2 with goodaccuracy.

[0032] The guide rails are normally in their reference positions, forexample at the lower part of each main rail 7. According to the method,the robot starts its setting procedure of the device by, for a firstmain rail 7, searching for the first available guide rail 8 on the mainrail. This is performed by the robot having already changed tool since asetting tool 16 is connected to the tool shunter on the robot hand 17.The setting tool 16 is a mechanism designed for engaging with the fixingelement 9. Engagement is possible since the setting tool 16 is equippedwith a male part 19 and the fixing element with a female part 20, whichtogether comprise a coupling, and which engage with high precision witheach other. The coupling contains connections for a pressure medium thatcan be conveyed between the robot and the tool for performing unlockingof the above mentioned locks on setting a fixing element, and locking ofcorresponding locks when the fixing element is placed in the correctposition. When the first guide rail 8 has been found and the settingtool 16 on the robot hand is attached to the fixing element 9, both themain rail 7 lock and the guide rail 8 lock are unlocked.

[0033] In its control system, the robot has position data in the form ofco-ordinates in x, y and z directions for the fixing element 9 of itsassociated guide rail 8 which the robot is holding at the moment,thereby allowing the robot to freely move the fixing element in the saidthree directions. This permits the main rail 7 to slide in the xdirection, when the correct x co-ordinates are entered, and the guiderail 8 to slide in the y and z directions, when y and z co-ordinates areentered. When the robot has moved the fixing element 9 to itspredetermined position, both the main rail and the guide rail are lockedagain. The control system then supplies the robot with data on theposition of the next guide rail 8 on the same main rail as before,whereby the robot searches for the new guide rail, connects itself to itand moves, this time in the y and z directions only, the guide rail'sfixing element 9 to the predetermined position. In this case, the lockfor the main rail 7 is never unlocked. It is only the guide rail that isslid in the y and z directions. For the remaining guide rails 8 on thesame main rail 7, a similar procedure is followed.

[0034] When all used fixing elements 9 on a main rail 7 are positioned,an equivalent procedure is carried out for the other main rails 7 usedon the rig, with their accompanying guide rails and fixing elements 9.

[0035] When all fixing elements 9 on the device are positioned accordingto the predetermined data, mounting of, for example, airframe frames tothe device can commence. According to the example, a frame 21 is mountedon the fixing elements 9 located on the same main rail, so that allframes are held in place within the required limits of tolerance andtogether define the desired airframe profile. An airframe skin 22 in oneor more sections is fixed at several points and then fastened to thepreviously secured frames. Next, frames and skin can be put togetherusing screws, rivets or with equivalent fastening devices. As mentionedearlier, the method in accordance with the invention has the advantagethat the industrial robot used for regulating the device may also beused as an assembly robot for fastening together the frames and theskin, where the robot is used for drilling holes, as well as screwing orriveting.

[0036] The fixing element 9 may be replaced, so that it can be adaptedto different types of fixed objects, such as frames or skins.

[0037] A variation of the invention is to use a semi-flexible solutionwhere a portal robot used as a manipulator for setting the fixingelements can run alongside the rig and perform the procedure for settingthe fixing elements. In this case, the manipulator cannot be used forany other operations, although there is still the advantage, incomparison to known techniques, that the fixing elements may bepositioned freely within the space volume given by the device.

[0038] In a further variation of the invention the manipulator can beembodied by a manual manipulator, which would then be designed as a handtool, and which in a way corresponding to that described above for therobot hand 17 is calibrated against the device's calibration plate 18and is connected to the fixing elements 9. On a display connected to thehand tool, the position of the fixing element to which the hand tool isjoined is read, whereby it is possible, after unlocking the said locksin a way similar to that done by the robot 1, to move the tool to aposition where the tool moves the fixing element 9 to the desiredposition in x, y and z directions. When the desired position isachieved, the rails are locked in the same way as presented above. Toensure accuracy in the setting procedure when using the hand tool, itmay be suspended from a balancing mechanism that can move alongside therig in the x and y directions. Measurement of the position of the handtool in relation to the device is in this case carried out by a laserposition sensor, which measures by laser the hand tool's position interms of the three space co-ordinates and shows the current position ofthe hand tool, or rather the position of the attachment point for thefixing element being held by the hand tool, on a display so that theoperator of the hand tool can continuously monitor the said currentposition and make the necessary movements of the hand tool to achievethe desired position of the fixing element 9.

[0039] For the examples described above, it has been mentioned that thepositions of the fixing elements are set based on three co-ordinatesthat are assumed to be oriented perpendicular to one another. However,it is also possible to use other co-ordinates, oriented at differentangles to each other than those adopted above.

1. A method for regulating a device (2) used for assembling aircraftairframe pieces, where the device consists of a rig (3) comprising mainrails (7) that can slide parallel to each other alongside the rig (3)along a first co5 ordinate x, and on each main rail (7) a number ofguide rails (8) which can both slide parallel to each other along themain rail (7) along a second coordinate y, and axially along a thirdco-ordinate z, and with a fixing element (9) at the end of the guiderail (8), where the method involves the following steps: a) amanipulator (1) grasps a guide rail's (8) fixing element (9) after whichthe fixing element (9) is moved by the manipulator (1) in directions x,y and z so that the fixing element (9) is made adopt a predeterminedposition in space, b) the position of the fixing element (9) in space islocked in relation to the rig (3) by an automatic locking function, c)steps a and b are repeated for a predetermined number of fixing elements(9).
 2. Method as in claim 1 for the said regulating of the device (2)comprising the steps: a) the fixing element is grasped and moved by themanipulator while during the movement of the fixing element: a1) themain rail (7) to which the fixing element (9) is connected is slidparallel to the x direction, a2) the guide rail (8) to which the fixingelement (9) is connected is slid parallel to the y direction, a3) theguide rail (8) is slid axially in the z direction so that its fixingelement (9) is set at a given z co-ordinate, a4) when the fixing element(9) has adopted its predetermined position the main rail (7) and theguide rail (8) are locked by the said automatic locking function, b) fora guide rail (8) on main rail (7), a manipulator (1) grasps a guiderail's (8) fixing element (9) after which the fixing element (9) ismoved by the manipulator (1) in directions x, y and z so that the fixingelement (9) is made adopt a predetermined position in space, and whileduring the movement of the fixing element (9): b1) the guide rail (8) towhich the fixing element (9) is connected is slid parallel to the ydirection, b2) the guide rail (8) is slid axially in the z direction sothat its fixing element (9) is set at a given z co-ordinate, b3) whenthe fixing element (9) has adopted its predetermined position the guiderail (8) are locked by an automatic locking function, c) steps a and bare repeated for each main rail (7).
 3. Method as in claim 1 or 2, wheresetting of the fixing elements (9) is done by means of a separateindustrial robot, which herein constitutes the said manipulator (1). 4.Method as in claim 3, where the robot control system retrievesinformation on the position of the rig (3) from at least one referencebody (18) located on the rig (3).
 5. Method as in claim 1 or 2, wheresetting of the fixing elements (9) is done by means of a portal robot,which herein constitutes the said manipulator (1) and which is arrangedso that it straddles the rig (3) and is capable of running alongside therig (3).
 6. Method as in claim 1 or 2, where setting of the fixingelements (9) is done by means of a hand tool, which herein constitutesthe said manipulator (1).
 7. Method as in claim 6, where the position ofthe hand tool is measured by a measuring device, such as a laserinstrument.
 8. Method as in claim 7, where, during the device regulatingprocedure, the hand tool is supported by a supporting device that can bemoved along the rig (3).
 9. Method as in claim 2, where the fixingelement (9) has a coupling part (19) and the manipulator has acomplementary coupling component (20), which couple with each otherduring regulating of the device (2).
 10. Method as in claim 9, where acoupling created by the said coupling components (19, 20) has means fortransferring a medium that activates or deactivates the lock or locksthat are associated with the fixing element (9) that is being set by themanipulator (1), and where the said medium is supplied by themanipulator (1).
 11. A device used for assembling aircraft airframepieces, characterised in that the device consists of a rig (3)comprising main rails (7) that can slide parallel to each otheralongside the rig (3) along a first co-ordinate x, and on each main rail(7) a number of guide rails (8) which can both slide parallel to eachother along the main rail (7) along a second co-ordinate y, and axiallyalong a third co-ordinate z, and at the end of the guide rail (8) thereis a fixing element (9).
 12. Device as in claim 11, characterised inthat the main rails can slide in such a way that a number of fixingelements (9) attached to the rails (7, 8) can be positioned freely inthree co-ordinates x, y, z in space within a given volume.
 13. Device asin claim 11, characterised in that the ends of the main rails (7) canslide in parallel arranged beams (5, 6), which make up a part of aframework in the rig (3).
 14. Device as in claim 13, characterised inthat the ends of the main rails (7) are equipped with locks, whereby themain rails may be locked to the said beams (5, 6).
 15. Device as inclaim 13, characterised in that the guide rails (8) are arranged in acarriage (10), where the carriage (10) slides along the main rail (7) bymeans of guides (11), and where the guide rail, by means of slidingbearings, can move relative to the carriage in its axial direction. 16.Device as in claim 15, characterised in that the carriage (10) isequipped with locks, whereby the carriage (10) is locked to the mainrail (7) along which the carriage (10) runs, and the guide rail (8)running in the carriage (10) is locked to the said carriage (10). 17.Device as in claim 14 and 16, characterised in that the locks are openand closed by means of pneumatic, hydraulic or electrical powertransmission.